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  1. #1
    FEP Member vdubn's Avatar
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    Default Body Cracks, Best Way to Repair

    I had looked all over the top side of the pan, and hadn't seen anything... the car was full of a bunch of stuff, so not too surprising that I missed it. Anyway, I found the following cracks at the back of the tunnel. I will be installing weld-in subframe connectors after I get the drivetrain back in, so hopefully I won't seeing any new ones show up. After really looking the car over tonight, these three look to be the only cracks on the whole car.

    So, I have a MIG welder, and could just stitch these from inside the car, but I wanted to see if anyone had any recommendations for the best way to reopair these.

    Under the car:
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  2. #2
    Moderator wraithracing's Avatar
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    That looks like a bit more than just cracked sheet metal. It appears that there is damage to the metal that caused the stress cracks.

    First I would try to push/hammer/move the sheetmetal back into it's original position. Then I would most likely use a cut off wheel and slice the cracks. All you want to do is open up the crack with a thin cut off wheel (No more than 1/8"). Then use a Mig welder and weld the new cuts back up and slightly longer than the full crack. That will give you the best strength and should prevent the cracks from returning.

    You can just weld over the cracks, but in my experience the small cut with a cut off wheel gives you a better surface for welding and allows the new weld metal to penetrate further rather than just sitting on top of the cracked metal. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

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  3. #3

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    Holy Rear-Ender Batman! That car has been hit by a Semi Tractor Trailer. As far as the cracks go, those are pretty minor. These cars were famous for that. Supposedly the floor pan was a bit stronger starting in 1984, you don't say what year this is. And there are some extra braces in the SSP cars as well. You say you are adding SFC and that will be a HUGE improvement.

  4. #4
    FEP Member vdubn's Avatar
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    Yea, I checked the car all over, and there are no signs of any accidents. The crack at the back of the hump, in the wrinkles, looks like its right at the spot where the floor was stamped, and it wrinkled from the factory. The car is an 85 GT.

    Trey, I agree with making some small V's out of the cracks, thats a great idea. Some research last night showed that folks drill an 1/8" hole at each end of the cracks, to prevent them from spreading, then just using the MIG to fill them in. I figure welding from the top/inside of the car would be easiest, and most effective.

  5. #5
    Moderator wraithracing's Avatar
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    The 1/8" hole at the ends works too when not making the cuts. I would consider that on the smaller cracks since that would be easier and quicker. I would still do the cuts on the larger cracks to make sure you get a good weld and actually fuse the metal back together rather than just add some on top of the issue.

    Anything you can weld from inside will always be easier than overhead welding, so I highly recommend that. Luckily if you do have to weld up some of that from underneath they are small areas so you shouldn't have a huge issue. Just give it enough heat for proper penetration and enough wire speed and you will be fine. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
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    Current Capris:
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    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
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  6. #6
    FEP Senior Member droopie85gt's Avatar
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    I would drill the small holes. They turn the straight line stress crack into an arc which is supposed to resist stress cracks better. What I've read is if you don't drill the holes eventually the stress crack will continue out past the weld. I watched a documentary on the Titanic and they dove on the wreck of it's sister ship and noticed that they had made an undocumented change to the expansion joints. On Titanic they were straight, but on Britannic, evidently Harland & Wolfe was worried the Titanic broke in two pieces because of a stress crack at the expansion join. When they dove on it, the expansion joint looks like an upside down old style thermometer. They said the round part was to spread out the stresses and keep a crack from forming.

    I've got an 85 and I keep finding cracks!! I fixed some on the upper torque boxes and when I went to sound proof the floor, I found some under the driver's seat.
    1985 GT, Sunroof, 5 Lug, Rear Discs, 01 Graphite Bullets, 88 forged piston shortblock, 2.02/1.60 Alum heads, Weiand Stealth, Holley C950 TBI, BBK Long tubes

  7. #7
    Moderator wraithracing's Avatar
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    Cutting the cracks with a cut off wheel do essentially the same thing. The end of the cut will be roughly a half circle shape that is similar to that of a drilled out.

    The advantage of making the cut is that down you are joining the metal back together with a nice weld bead that fuses the two sides of the crack without the stress of the cracked metal. This also forces the weld into the panels rather than sitting on top of it.

    Stress cracks were only part of the equation as to why the Titanic sunk. Even doing the same type of joint of the Britannic on the Titanic most likely would not have prevented it sinking, but that is a WHOLE different discussion.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  8. #8
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    My 84 T Top has the exact same cracks , in the same place .
    Never been wrecked ( i am the second owner ) , and the floor looks very much the same as well .
    Assembly line workers , and the tools they had to work with , at that time , were far from quality , but i am not complaining.
    Still enjoying what they got right , and changing what they didnt .
    clowns to the left of me , Jokers to the right

  9. #9
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    I did the drill method over the cutoff wheel, but either work. Make sure you use a welding copper spoon on the back of the panel. It makes it a lot easier to not blow through the metal by accident.

    Here's my work on the notchback I'm building.
    https://youtu.be/L5hSFb2M2CI
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  10. #10
    FEP Member vdubn's Avatar
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    How crazy... I just watched that video the other day.... nice job! And a fellow Oregonian.... your video is where I got the idea for the drill method. Going to run over to the welding shop today to grab a copper spoon, as I need to also weld back in an inner fender panel that the previous owner cut out. I think I will need some strips of metal on the back side to fill these gaps though... your opinion would be appreciated.

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  11. #11
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    If you tack weld that panel back into place , as you go , hammer and dolly , to make a nice fit .
    No need for backing strips .
    Slow and steady .
    clowns to the left of me , Jokers to the right

  12. #12
    FEP Member vdubn's Avatar
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    A couple of the cuts are more than 1/8", and for the thinner stuff I was still having some issues getting it to bridge the gap. I was mostly looking at using some metal strips behind the large gaps.

  13. #13
    FEP Power Member dagenham's Avatar
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    You basically have to weld a bead to another bead and you should be able to fill the gap without using any backing strips. And remember, if your welds are right, the weld bead is just as strong if not stronger than the surrounding metal.

  14. #14
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    Quote Originally Posted by ashley roachclip View Post
    If you tack weld that panel back into place , as you go , hammer and dolly , to make a nice fit .
    No need for backing strips .
    Slow and steady .
    I agree with this advice. The only part that may give you trouble is the front cut on the bottom. The gap is pretty big, but with a copper spoon on the back you should be able to slowly build a bridge across the pieces. A strip on the back will do the same thing, basically offer a bridge to span the gap. Just take your time and you'll have it done in no time.
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  15. #15
    FEP Member vdubn's Avatar
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    Well, on the narrower gap parts, it went well, on the wider gap, even with the copper spoon, just kept blowing holes in the metal. I backed my feed and current way down, and still no luck.

    As for the cracks, I will take it slow, and since they are butted well, I think they should be easy to weld up... I am just nervous based on how easy the engine panel was to blow through... hoping not to blow through the floor pan.

    I was able to get the extra 4 holes per strut tower filled... and they came out well. I still have a hole on the drivers side fender support, will try to get it welded up soon as well.

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  16. #16
    FEP Senior Member droopie85gt's Avatar
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    Quote Originally Posted by wraithracing View Post
    Stress cracks were only part of the equation as to why the Titanic sunk. Even doing the same type of joint of the Britannic on the Titanic most likely would not have prevented it sinking, but that is a WHOLE different discussion.
    Haha..I just saw this. It sank because of a big hole in the side letting so much water in it became less boyant than water.

    Back on topic to VDUBN. Looks like you are making good progress! Somehow, I need to make progress on my own junk.
    1985 GT, Sunroof, 5 Lug, Rear Discs, 01 Graphite Bullets, 88 forged piston shortblock, 2.02/1.60 Alum heads, Weiand Stealth, Holley C950 TBI, BBK Long tubes

  17. #17

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    Very nice work, vdubn - especially on the shock towers.

    I found similar cracks in my 'vert's floor pan. I think I will follow the advice here and drill/cut/weld them up over winter.

  18. #18
    FEP Member vdubn's Avatar
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    Thanks... I was able to weld up the floor tonight, and it came out ok. Not quite as pretty as I would like, but the first one looked amazing, the others were a little tougher and I blew through in a couple spots, so had to build up a bit.

    I got good penetration, so I feel like these will hold well.

    Start with the pretty one:

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    In this one, on one edge it looks like there is a line there, but its just the edge of one of the welds. I looked under the car, and the penetration is good and consistent.
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    Last edited by vdubn; 09-01-2017 at 01:00 AM.

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